Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$19.99	10.485%	$22.086	$22.09	$22.10	$22.10
Purchase #2	$146.78	11.160%	$163.1606	$163.16	$163.15	$163.20
Purchase #3	$234.77	8.863%	$255.5777	$255.58	$255.60	$255.60
Purchase #4	$249.28	12.676%	$280.8787	$280.88	$280.90	$280.90
Purchase #5	$210.43	10.314%	$232.1338	$232.13	$232.15	$232.10
Purchase #6	$103.49	7.796%	$111.5581	$111.56	$111.55	$111.60
Purchase #7	$235.87	11.853%	$263.8277	$263.83	$263.85	$263.80
7 purchase totals =	$1,200.61		$1,329.2226	$1,329.23	$1,329.30	$1,329.30